For the first time, a team of Japanese researchers have been able to sequence the complete genome of the Pacific bluefin tuna (Thunnus orientalis) and to identify the genes that are responsible for its remarkable eyesight. This feature has turned this species into an extremely efficient predator in the ocean.

In their study, published in the Proceedings of the National Academy of Sciences, using next-generation sequencing technology, the scientists have singled out several retina genomes. They then compared the genes of several fish species and found the Bluefin tuna to be the most developed.

From a total of 26,433 protein-coded genes, five common fish visual pigment genes were identified, one of them being the green-sensitive (RH2) opsin gene. Pacific bluefin tuna has at least five copies of the RH2 opsin gene, the most evolved among the fish analysed by the scientists.

Further analysis revealed that this species of tuna has undergone a unique evolution which may have helped develop its sharp vision, the most acute of all vertebrate fish, according to the genome study. This makes it a deadly oceanic predator as the bluefin tuna can measure the distance to prey and easily detect it.

“We now know that the tuna has excellent colour recognition,” says Mitsuru Ototake, chief of the Fishery Reserach Agency ’s Research Centre for Aquatic Genomics. “We may be able to reduce collision deaths if we conduct further research on colours tuna can clearly see.”

The bluefin tuna is of special interest due to its expensive price in the market. In Japan, where prices at Tokyo’s famous Tsukiji fish market can fetch a record-breaking USD 736,000 for a single fish, it is considered a delicacy. Overfishing and exploitation have caused concern over the future of this species and it is hoped that the study will help with conservation issues and better ocean-wide resource management.

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